Packer Backup Ring with Closed Extrusion Gaps

ABSTRACT

Alternating l-shaped side slots are cut into opposed sides of a backup ring and are circumferentially offset and alternately extend from the inside and outside dimension. An oval shaped opening connects adjacent circumferentially offset slots so that on ring expansion the inside and outside diameters increase as the openings are sheared at one end to place a barrier in opened side slot to prevent extrusion of the adjacent sealing element.

FIELD OF THE INVENTION

The field of the invention is sealing systems for subterranean tools against tubular or open hole or cased hole and more particularly anti-extrusion barriers for low, medium and extended reach for a seal element.

BACKGROUND OF THE INVENTION

In the unconventional drilling and completion industry, oil and gas deposits are often produced from tight reservoir formations through the use of fracturing and frack packing methods. To frack a well involves the high pressure and high velocity introduction of water and particulate media, typically a sand or proppant, into the near wellbore to create flow paths or conduits for the trapped deposits to flow to surface, the sand or proppant holding the earthen conduits open. Often, wells have multiples of these production zones. Within each production zone it is often desirable to have multiple frack zones. For these operations, it is necessary to provide a seal known as a frack packer, between the outer surface of a tubular string and the surrounding casing or borehole wall, below the zone being fractured, to prevent the pumped fluid and proppant from travelling further down the borehole into other production zones. Therefore, there is a need for multiple packers to provide isolation both above and below the multiple frack zones.

A packer typically consists of a cylindrical elastomeric element that is compressed axially, or set, from one end or both by gages within a backup system that cause the elastomer to expand radially and form a seal in the annular space. Gages are compressed axially with various setting mechanisms, including mechanical tools from surface, hydraulic pistons, atmospheric chambers, etc. Setting typically requires a fixed end for the gages to push against. These fixed ends are often permanent features of a mandrel but can include a dynamic backup system. When compressed, the elastomeric seal has a tendency to extrude past the gages. Therefore, anti-extrusion backups have become common in the art. However, typical elastomeric seals maintain the tendency to extrude through even the smallest gaps in an anti-extrusion backup system.

In cased-hole applications, anchoring of compression set packers is a common feature in the completion architecture. Anchoring is provided by wedge-shaped slips with teeth that ride up ramps or cones and bite into the casing before a packer is set. These systems are not part of the backup system nor are they designed to provide anti-extrusion. Often they are used in the setting of the packer to center the assembly which lowers the amount of axial force needed to fully set the elastomer seal. Once set, anchoring systems are also useful for the life of the packer to provide a uniform extrusion gap, maintain location and help support the weight of a bottom-hole assembly in the case of coiled tubing frack jobs. Anchors also prevent tube movement in jointed strings resulting from the cooling of the string by the frack fluid. Movement of the packers can cause them to leak and lose seal.

In open-hole frack pack applications it is rarer for the packer to have anchoring mechanisms, as the anchor teeth create point load locations that can overstress the formation, causing localized flow paths around the packer through the near well-bore. However, without anchors, movement from the base pipe tubing can further energize the elastomeric seal. Energizing the seal from tube movement tends to overstress the near wellbore as well, leading to additional overstressing of the wellbore, allowing communication around the packer, loss of production, and potential loss of well control to surface. However, the art of anchoring has been reintroduced in new reservoirs in deep-water open-hole fracking operations. The current state of the art in open-hole frack pack operations requires a choice between losing sealing due to anchor contact induced fractures, packer movement, or over-energizing of the elastomeric element.

Extrusion barriers involving tapers to urge their movement to block an extrusion path for a sealing element have been in use for a long time as evidenced by U.S. Pat. No. 4,204,690. Some designs have employed tapered surfaces to urge the anti-extrusion ring into position by wedging them outwardly as in U.S. Pat. No. 6,598,672 or in some cases inwardly as in U.S. Pat. No. 8,701,787. Other designs simply wrap thin metal rings at the extremities of the sealing element that are designed to contact the surrounding tubular to create the anti-extrusion barrier. Some examples of these designs are U.S. Pat. No. 8,479,809; U.S. Pat. No. 7,708,080; US 2012/0018143 and US 2013/0147120. Of more general interest in the area of extrusion barriers are U.S. Pat. No. 9,140,094 and WO 2013/128222.

In some applications the gap across which the seal is expected to function is quite large placing such applications beyond the limits of the design in U.S. Pat. No. 6,598,672. There is a need for an extended reach design that can withstand the pressure differentials. The present invention addresses this need with slots that extend toward each other from opposing faces and are circumferentially offset. The slots are connected at voids that extend from the original inside to the original outside diameter. Expansion of the ring allows alternating voids to separate or shear at the outside and the inside diameter so that as gaps form in the ring a segment of the ring presents itself in each of the opened gaps as both the inside and the outside diameters increase. In an alternative solution to extrusion through a backup ring a backup ring with a common base has multiple rows of extending segments with gaps in one row offset circumferentially with gaps in an adjacent row. The common base lends structural integrity to the backup ring design and reduces the risk that relative rotation can occur between adjacent rows that would tend to align the offset gaps from one row to the next. These and other aspects of the present invention will be more readily apparent, to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while understanding that the full scope of the invention is to be determined from the appended claims.

SUMMARY OF THE INVENTION

Alternating l-shaped side slots are cut into opposed sides of a backup ring and are circumferentially offset and alternately extend from the inside and outside dimension. An oval shaped opening connects adjacent circumferentially offset slots so that on ring expansion the inside and outside diameters increase as the openings are separated or sheared at one end to place a barrier in opened side slot to prevent extrusion of the adjacent sealing element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a backup ring in a run in position;

FIG. 2 is a side view of the ring of FIG. 1;

FIG. 3 is the view along line 3-3 of FIG. 2;

FIG. 4 is the view along line 4-4 of FIG. 2;

FIG. 5 is an outside diameter view of the backup ring in an expanded position;

FIG. 6 is an inside diameter view of the backup ring in the expanded position;

FIG. 7 is a side view of the backup ring in the expanded position;

FIG. 8 is a section view of a backup ring showing the layers of ring segments extending from a common base;

FIG. 9 is an isometric view of the backup ring of FIG. 8

FIG. 10 is a section view of the backup ring of FIG. 8 in a run in position;

FIG. 11 is the view of FIG. 10 in the set position;

FIG. 12 is an expanded view of the view on FIG. 1;

FIG. 13 is an expanded view of the view in FIG. 2;

FIG. 14 is a section view of a packer in the run in position using the backup ring;

FIG. 15 is a set position of the view in FIG. 14;

FIG. 16 is an exterior view of the view in FIG. 15;

FIG. 17 is an alternative to the dog leg slot design in FIG. 1 using a dovetail configured to allow relative circumferential movement for an increase in diameter;

FIG. 18 is a close up view of FIG. 17 to show the dovetail has initial gaps to allow for the relative circumferential movement at the inside and the outside diameters;

FIG. 19 is the view of FIG. 17 after the diameters are increased;

FIG. 20 is an enlarged view of FIG. 19 showing the dovetail acting as a relative circumferential movement travel stop and gap barrier at the same time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 10 and 11 illustrate the juxtaposition of a sealing element 10 next to a backup ring 12. FIG. 2 shows an end view of a continuous single ring 14 that can be disposed next to a sealing element 10. Ring 14 has an inside diameter 16 and an outside diameter 18. There are alternating l-shaped slots 20 and 22 that start at the outside diameter 18 and at the inside diameter 16. FIG. 2 shows a tapered or sloping side 24 and slots 20 and 22 that alternate as to the location of the long dimension of the l-shaped slot. Sloping side 26 is not seen in FIG. 2 but is shown as FIG. 3 as well as the cylindrically shaped inside surface 28 that defines the inside diameter 16. FIGS. 1 and 4 both show an outside view where it is seen that slot 22 is a segment that goes to outside diameter 18 has a continuation slot segment 22′ that is circumferentially offset a few degrees. Slots 22 and 22′ are at opposed ends of an oblong bore 22″ that may have internal supports. Bore or opening 22″ is seen at an opposite end at inside diameter 16 in FIG. 3. When ring 14 is increased in both inside diameter 16 and outside diameter 18 the bore undergoes hoop stress and comes apart at outside diameter 18 when outside diameter 18 grows as shown in FIG. 5. The connecting bore 22″ has separated or sheared leaving surface 30 as a closing wall to a gap 32 that opens and into which the sealing element 34 can move. However, since the gap 32 is closed by surface 30, migration of the sealing element 32 in the direction of arrow 36 is stopped by surface 30. At the same time should there be a sealing element 38 on an opposite side of ring 14, the searing apart of bore 22″ at the outside diameter 18 also leaves surface 40 at the end of gap 42 to stop movement of seal 38 in the direction of arrow 44.

Bores 20″ are seen as alternating with bores 22″ at the outside diameter 18 as seen in FIG. 1 and are seen at inside diameter 16 in FIG. 3 as connecting slots 20 and 20′ in the run in condition. FIG. 6 shows bores 20″ separated or sheared from hoop stress during radial expansion of inside diameter 16. Surfaces 50 and 52 are presented respectively at the ends of widened slots 54 and 56 from the inside diameter 16 radial expansion. As a result, a sealing element 58 will be blocked from passing surface 50 in the direction of arrow 62 or/and a sealing element 60 will be blocked by surface 52 when moving in the direction of arrow 64 under differential pressure that would otherwise allowed for extrusion in gaps closed at the inside diameter by surfaces 50 and 52 as a result of separating or shearing of bores or openings 20″ at inside dimension 28. Note that at inside dimension 28 bores 22″ do not separate or shear as they are supported at that location by the ring structure unlike bores 20″ that span slots 20 and 20′ at inside dimension 28.

Note that as shown in FIG. 6 opposed surfaces 50 and 54 may separate circumferentially to leave a small gap or their ends can alternatively align or overlap and may also optionally involve a stop or overlap to limit the relative circumferential movement between surfaces such as 50 and 54 at inside surface 28 to insure that any gap such as 54 and 56 are fully closed at maximum condition for inside diameter 16. This is equally true at outside diameter 18 shown in FIG. 5 where surfaces 30 and 40 circumferentially separate to an end position where there is overlap between them, a small gap or alignment between their ends so that there is no effective gap in the directions of arrows 36 and 44. Alternatively opposed surfaces 30 and 40 can have one or move travel stops 31 to limit the amount of relative circumferential movement to an overlapping position as shown in FIG. 5.

FIG. 7 shows how surfaces 30 and 50 close off gaps 32 and 54 respectively when in the inside diameter 16 and the outside diameter 18 are increased. It also shows the short slot segments that make the l-shape 70 and 72 that are there to reduce stress concentration at ends of opening gaps such as 32 and 54, for example.

FIG. 12 is similar to FIG. 5 and represents the gaps closed with end walls 30 and 40 after the inside and outside diameters are enlarged, as previously described. FIG. 13 is the view of FIG. 2 after the inside and outside diameters are enlarged graphically illustrating the alternating pattern of opened gaps on the inside diameter and the outside diameter with the extrusion gaps closed using a single ring that can grow in outside diameter, for example from 8.3 inches to 9.875 inches while closing extrusion paths.

FIGS. 17-20 are an alternative design using the concepts of the design in FIGS. 1-7 but instead of l-shaped slots with a dog leg that starts out as a bore but then separates or shears to create relative circumferential movement to produce end walls to close gaps that enlarge at the inside and the outside diameters, uses slots that are interacting dovetail shapes that alternatively start at the inside diameter and the outside diameter and do not go all the way through. Diameter enlargement at the inside and the outside diameters is enabled in a relative circumferential direction until one part of the dovetail closes an initial dovetail gap. The dovetail limits the ring gaps and acts as an extrusion barrier by its presence in those enlarging gaps that open alternatingly from the inside and outside diameters. FIGS. 17 and 18 show the initial gaps 80 between the male 82 and the female 84 components of each dovetail. FIG. 20 shows gap 80 closed during diameter expansion at the inside and the outside diameters. An extrusion gap such as 86 opens but the male component 84 is in that gap to close it up. The same condition happens at the inside dimension and the outer dimension of the backup ring as previously described in the context of FIGS. 1-7. Bores 88 do not open on the outside diameter as between FIGS. 17 and 19 but on the inside diameter that is not shown for this variation there is relative circumferential movement until the counterpart dovetail on the inside diameter closes an initial dovetail gap that defines the end of relative circumferential movement where gaps open on the inside dimension. In the sense of alternating gaps that open from the inside and then the outside diameters the embodiments of FIGS. 1-7 and 17-20 operate the same way. Instead of bores separating or shearing to enable circumferential growth the slack in dovetails closed to enable circumferential growth at the inside and the outside diameters. FIGS. 17-20 are schematic and can illustrate the view at an outer diameter or an inner diameter. The operating principle is the same as previously described for FIGS. 1-7 in that gaps alternatingly open up in a circumferentially offset manner on the inside and the outside dimensions and the gaps so created are then closed to seal element extrusion. In the case of FIGS. 1-7 a wall surface is interposed in the gap due to the alternating gaps opening up and in FIGS. 17-20 the dovetail itself allows the gaps to open up until slack in the dovetail is removed at which time the male portion of the dovetail is interposed in the gap to block it entirely or at least substantially.

FIGS. 14-16 show a typical packer in the run in and set positions using the ring 14 as a backup ring. FIG. 16 graphically shows how the dog leg slots that open on the outside diameter block the extrusion of the sealing element as previously described. Details of the operation of the rings 90, 92 and 94 can be reviewed in U.S. application Ser. No. 14/989,199 that is fully incorporated herein as if fully set forth. While that design featured alternating gaps opening on the inside diameter and the outside diameter, there was no feature of blocking the opened gaps against extrusion.

FIG. 8 illustrates a backup ring design featuring a common base ring 100 that has multiple segmented rings 102 integrally extending therefrom, with 2-4 being preferred. The segmented nature of each ring can be seen in FIG. 9 in the form of offset gaps 104 and 106 in adjacent rings. Preferably there is a circumferential offset of about 12 degrees between gaps on adjacent rings. Each ring has multiple gaps that are all offset from gaps on an adjacent ring on either side. Because the segments that make up each ring are integrally connected to the base ring 100 there is no relative rotation among the stacked segmented rings 102 and the rings 102 are still flexible as seen by comparing FIGS. 10 and 11 for the run in and the set positions. Since the stacked rings 102 are supported circumferentially along the length of each ring segment from base 100 the assembly of rings also has greater resistance to extrusion when pushed against the surrounding tubular as shown in FIG. 11. Ring segments 102 extend to different axial lengths for running in and have a free end that is offset and axially aligned with an axis of ring 100. Gaps 104 are as long axially as said segments 102. An internal groove 108 holds a mandrel seal 110 to prevent extrusion of sealing element 10 along the mandrel.

Those skilled in the art will appreciate that alternative backup ring designs are described that have the objective of dimensional growth while limiting or eliminating extrusion of a sealing element on preferably opposed ends of a sealing element. In FIGS. 1-7 alternating circumferential slots with dog leg connectors in the form of a bore extend from the inside diameter and the outside diameter in alternating fashion. On radial expansion the bores separate or shear on surfaces where the bore is a connector to slots that extend from opposed ends of an outer or inner diameter and where the two slots are themselves circumferentially offset by the width of the oblong bore or void. As a result the inside and outside diameters grow as the slots part to form gaps and the offset disposition of slots connected by an oblong bore allows an end surface to be positioned in each gap that minimizes or completely prevents seal element extrusion. The dimensional growth need not be uniform so that the enlarged dimension can conform to an irregularly shaped borehole wall, for example. The adjacent and oppositely facing end walls can interact with each other as a given oblong opening is separated or sheared to expose such end walls so that there is overlap between such adjacent end walls with a stop device that limits relative circumferential movement between them. Alternatively the wall ends can align or pull away from each other slightly so that there is either no extrusion gap or a minimal gap for the sealing element.

The same pattern of slots that open into gaps alternating on the inside and outside diameters can be used with dovetail cuts that have slack in them in the run in diameter and where the relative circumferential movement of each pair of dovetail components is limited by the slack coming out of each dovetail connection. The gaps that open are blocked by the extension of the male of the dovetail pair extending into the opening. The dovetail pairs start in an alternating pattern on the inside and outside diameters to present a cohesive ring structure that can expand on the inside and outside diameters. The dovetail slots on the inside diameters are circumferentially spaced from the dovetail slots on the outside diameter and the gaps that form as the diameters increase are substantially blocked by the male dovetail component bottoming on the female surrounding component or when the outside dimension of the backup ring engages a surrounding tubular, whichever happens first. The structure with alternating dog leg slots or dovetail slots lets the ring remain whole while lending the ring flexibility of going out of round so that if the surrounding tubular has dimensional imperfections, the backup ring can adapt to the actual shape of the inside wall of the surrounding tubular. A single ring can be placed between sealing elements and reduce or eliminate extrusion between the sealing element in either of opposed directions.

In a backup ring with multiple stacked rows of segmented rings the gaps in adjacent rings are offset and all the rings are preferably integral to a common ring base. The extrusion gaps are closed off while the integration of the stacked rings with the base provides for a stronger yet still flexible design that can conform to the surrounding tubular wall for closing an extrusion gap. The outer edge of the stacked rings is made long enough so that there is bending into a more parallel orientation with the surrounding tubular when the set position of FIG. 11 is reached. A support ring can backstop the backup ring in the set position on an opposite side from the sealing element as shown also in FIG. 11.

The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: 

We claim:
 1. A backup ring assembly for extrusion protection for a sealing element of a borehole barrier, comprising: a continuous ring having an inside and an outside surface and an axis; circumferentially spaced slots having a first end extending into said ring from said inside and outside surfaces and having a second end ending short of an opposing said inside or outside surface such that said ring can remain continuous as said inside and outside surfaces grow dimensionally by virtue of said slots opening gaps, said gaps substantially closed at one end by a portion of said ring for contacting the sealing element to minimize extrusion through said gaps.
 2. The assembly of claim 1, wherein: said slots on said inside and outside surfaces each formed by circumferentially spaced axially extending segments connected by a transverse opening in said ring.
 3. The assembly of claim 2, wherein: said transverse openings at each said slot comprise opposed ends at said inside and said outside surfaces.
 4. The assembly of claim 3, wherein: said openings are positioned midway on said inside and outside surfaces.
 5. The assembly of claim 3, wherein: said ends of said openings that join said respective segments shearing or separating to enable opening of said gaps.
 6. The assembly of claim 3, wherein: said ends of said openings that do not join said respective segments remaining intact when said inside or outside surfaces increase in dimension.
 7. The assembly of claim 2, wherein: said slots at an end away from said inside and outside surfaces comprising a stress reduction bend.
 8. The assembly of claim 1, wherein: said ring having a triangular cross-section such that said outside surface is wider than said inside surface.
 9. The assembly of claim 5, wherein: said transverse openings comprise an oblong shape so that said shearing or separating defines relatively moving opposed surfaces as said slots open to form said gaps.
 10. The assembly of claim 9, wherein: said surfaces are disposed at an internal end of said gaps that open from said slots.
 11. The assembly of claim 9, wherein: said relative movement of said opposed surfaces substantially blocks an internal opening in said gaps that open from said slots.
 12. The assembly of claim 9, wherein: said relative movement of said opposed surfaces is circumferential about said axis of said ring.
 13. The assembly of claim 9, wherein: said oblong opening shears at opposed ends to define said opposed surfaces.
 14. The assembly of claim 1, wherein: said slots define a dovetail shape of a male portion retained by a female portion with space in between said male and female portion to allow relative circumferential movement for enlarging said inside and outside surfaces as said gaps are created.
 15. The assembly of claim 14, wherein: said male portion extending into said gaps to substantially block an extrusion path for the sealing element.
 16. The assembly of claim 15, wherein: said gaps extending to varying sizes to allow said outside surface to conform to irregularities in the surrounding borehole.
 17. The assembly of claim 1, wherein: said gaps extending to varying sizes to allow said outside surface to conform to irregularities in the surrounding borehole.
 18. The assembly of claim 3, wherein: said openings are positioned offset from midway on said inside and outside surfaces.
 19. The assembly of claim 1, wherein: said ring having a multilateral cross-section. 